1. Field of the Invention
This invention relates to machine tools and more particularly to a sheet workpiece separation and feed device and method of sheet separation.
2. Prior Art
Recent developments in production engineering have emphasized the development of production process automation, utilizing unattended operation of production machines. Central to this concept is the use of computer controlled machines which are automatically supplied with workpieces by feeder mechanisms which are also under computer control. Although movement between successive machines can be accomplished in any of a number of various ways, common to such "automated factory" concepts is the necessity of supplying of an initial workpiece from a group of similar workpieces. Although this is principally a step to be performed at the initial stage of any production process, it also frequently repeats itself at various in-process storage points along the production flow.
When working with sheet material such as, for example, sheet metal or sheets of plastic or wood, there is a defined stage which is frequently encountered. This is a point where a stack of substantially similar sheets exists and where the sheets must be fed one at a time from the stack to a machine. This may occur initially at a point where the raw material sheets are being fed to the first production machine or it may occur at repeated points thereafter where partially worked sheets are stacked in holding areas between machines.
Automatic devices for supplying a sheet from a stack of sheets to a machine are well known. One particularly often used loader system in the machine tool industry which is utilized for supplying sheet material to fabricating equipment, such as punch presses, shears, blanking machines and the like, utilizes a top feed concept where the top sheet of a stack of sheets positioned in a storage area is lifted from the stack by a suction device and is thereafter transported by that device to a machine tool or machine tool group. An example of such a device is shown in U.S. Pat. No. 3,830,121 entitled "Installation for Cutting Rolled Sheets", issued Aug. 20, 1974. That patent illustrates a sheet feed mechanism for feeding a guillotine shear, the sheet feed mechanism including a swingable transfer arm from which vertically movable suction cups are suspended. The transfer arm initially positions the suction cups over a storage area where the cups are lowered onto the top sheet of the stack received in the storage area. After suction is applied, the suction cup set is lifted, thus lifting the top sheet. The swing arm then swings the suction set to a position over a feed mechanism. The suction set then lowers the sheet to the feed mechanism and the suction is terminated.
Another type of device, particularly adapted for use in connection with an auto gauging system which automatically gauges the sheet at the feed device, is shown in Canadian Pat. No. 1,077,387, issued May 13, 1980, and its counterpart United States patent application Ser. No. 52,241, filed June 26, 1979 as a continuation of U.S. Ser. No. 815,821, filed July 15, 1977, entitled "Automatic Load Unload Turret Punch", inventor Stephen C. Clark, all of which are assigned to the assignee of this application. Since the invention of the present application is usable in the device of the Clark U.S. application and Canadian patent, it will be described in connection therewith. For a more complete discussion of the loader mechanism, the teachings of the Clark application and patent are herein incorporated.
A common problem encountered with such suction lift and transfer devices when used in connection with sheet materials is the adherence of an underlying sheet to the top sheet. Since the suction operates only on the top sheet, except in those instances where slightly air pervious materials might be used as sheet material, the adherence of an underlying sheet is not caused by the application of the suction but rather by an underpressure or vacuum condition which may develop between the stacked sheets and which is particularly aggravated where fluids are applied to the sheets. It is common, particularly in connection with metals, for a lubricant or a preservative, or a combination of lubricant and preservative, to be applied to the sheets during their processing prior to stacking. This lubricant can be advantageous in the further processing of the sheet reducing friction as the sheet is worked on by the machine tools. However, it is a disadvantage when attempting to separate sheets, causing an underlying sheet or even sheets to adhere to or move with the sheet being lifted by the suction device.
Where magnetic materials are being worked on, it has been known to equip the transfer mechanism with separating devices known as fanning magnets, however, such magnets have little or no effect on non-ferrous materials such as, for example, aluminum, plastic, etc.
It would therefore be a noticable advance in the art to provide a non-magnetic system and method for assuring sheet separation in suction loading of workpiece sheets for supply to machine tools.